For the Old as Dirt party theme, you can make up your own saying inside an invitation that has a western motif or a cowboy boot or hat on it.  It should say something like, {Name}’s turnin’ 30, and that’s almost as old as dirt!  Head on over to the “3-0” corral and rustle up a good time on {date} at {time} {location}

You can consider attaching an ornament in the shape of a cowboy boot to it or add a plastic sandwich bag of dirt to it for added flair. 

Inside the invitation, request that people wear western clothing and bring anything they own that is “older than dirt” which can be outdated or worn out clothing to participate in a special ceremony.

For the black-and-white barbeque you can send out invitations that you have drawn up with a barbeque grill on the front and bordered by black and white checks.  The lettering should be in red to really stand out. 

This will give your guests some pretty good ideas about what kind of 30th birthday party they will be attending.  You can let them know that the attire for the party is casual, or come as you are.  Just because it’s a black-and-white barbeque doesn’t mean it’s a formal event.  If you don’t let them know this, some may get the wrong idea and come dressed formally and really feel out of place when they see everyone else dressed casually.